A modern motor-vehicle windshield frequently incorporates at least one AM antenna and one or more radio and TV antennas and even a grid of heating wires. Becoming increasingly widespread are diversity systems, where several antennas for the same frequency range are present on one antenna pane. In diversity operation, a diversity processor selects the antenna which possesses the most favorable reception properties and connects it to the receiver.
With such complex antenna systems, numerous faults can occur. These may result from defects in the antenna conductors forming the antennas, defects in the antenna/amplifier connections, defects of the amplifier, defects of the diversity processor, and defects in the connection with the receiver. To permit clear identification of the exact source of the malfunction, various diagnostic methods are known.
One diagnostic method known in practice, with which defects in the antenna conductors in the antenna pane can be determined, a transmitting antenna is arranged close to the motor vehicle, or is attached to it externally, and a test signal is applied to this transmitting antenna. The resultant antenna signal occurring in the individual antennas of the antenna pane are acquired with the aid of a diagnostic arrangement and are evaluated. Reliable, reproducible diagnosis is only possible however if the transmitting antenna is located at all times at a precise, reproducible position relative to the antenna pane and in addition if parasitic signals can be excluded to a maximum extent. The provision of corresponding facilities and suitable transmitting antennas and diagnostic equipment will generally present problems, particularly for small motor-vehicle repair shops.
In addition it is also known to use an ohmmeter to measure the electrical continuity of an antenna conductor up to the amplifier input. This assumes that the beginning and the end of the antenna conductor are accessible. Another known alternative consists of connecting a signal generator to the antenna connection conductor which has been extended out of the motor-vehicle antenna pane, and to measure the signal emitted by the antenna to be tested with a meter, which is laid on the outside of antenna pane along the antenna conductors as described in U.S. Pat. No. 4,276,509.